Construction of L-threonine overproducing strains of Escherichia coli K-12 using recombinant DNA techniques.

Abstract

The threonine operon of Escherichia coli was cloned in plasmid pBR322, using a threonine producing mutant, βIM4, as the DNA donor. A recombinant plasmid, pAJ294, that contains the whole threonine operon was obtained. No. 29-4, a transformant of βIM4 with pAJ294, had about eleven copies of pAJ294, five times higher homoserine dehydrogenase activity (coded by the thrA gene), and about three times higher threonine productivity than those of βIM4. No. 29-4 produced 13.4g/liter of L-threonine from 30 g/liter of glucose in the culture medium.